The structural embryology of fetal skin has been well studied and characterized; little is known about its function or biochemical characteristics. For this reason, fetal, neonatal and infant skin will be used to develop monoclonal antibodies to epidermal componentS of periderm, stratum intermedium, basal cells, basement membrane zone and congenital melanocytic nevi. Monoclonal antibodies will be generated by fusion of P3/NS1 (HGPRT-) mouse myeloma cells with the spleens of immunized mice. The mice will be immunized with human epidermal and dermal cellular components from tissues obtained from abortions, still births, neonatal deaths, neonatal foreskins and infants with congenital melanocytic nevi. Fused cells will be cultured in a media containing hypoxanthine, methotrexate and thymidine to exclude unfused HGPRT- P3/NS1 cells. Hybrid cells producing antibodies to the immunizing tissues will be cloned by dilution in individual culture wells. Those single colonies producing antibodies to the immunizing tissues will be evaluated for tissue specificity by radiommunoprecipitation and immuofluorescence against fetal, neonatal and adult skin and against human tissue culture cell lines. Monoclonal antibodies that are not against common cell surface antigens (Beta2 microglobulin, HLA) but are present in fetal and absent in more mature epidermis and those present in mature epidermis and absent in fetal skin will be studied further. The molecular weight and isoelectric point of the antigenic component reacting with the monoclonal antibody will be identified by SDS gel electrophoresis, electroblotting to nitrocelloluse paper and immunoperoxidase staining. Ultrastructural subcellular localization will be done by immunoelectron microscopy. Once developed, the specific monoclonal antibodies will be used to evaluate cutaneous neoplasms (squamous cell carcinoma, basal cell carcinoma, melanoma) non-neoplastic proliferations (keratoacanthoma, epidermal appendageal tumors, seborrheic keratosis, warts) and a broad range of other skin diseases (epidemolysis bullosa, psortasis, congenital melanocytic nevi). Correlation will be attempted between antigenic presence in fetal, neonatal or adult skin with function of epidermal cells. Current monoclonal and human antibodies will be used to evaluate fetal and neonatal skin for the presence of known antigens in order to establish sequence and progression of fetal development.